Cellar oil recovery by water displacement



April 2, 1963 M. H. GASKELL ETA]. 3,083,764

CELLAR OIL RECOVERY BY WATER DISPLACEMENT Filed Sept. 9, 1960 3Sheets-Sheet 1 on. wATER-: A -i FIG.I. H

INVENTORS. MERWIN H. GASKELL, DONALD C. LINDLEY, FREDERICK M.PERKINS,JR,

LI BY ATTORNEY.

April 2, 1963 M. H. GASKELL ET AL 3,083,764

CELLAR OIL RECOVERY BY WATER DISPLACEMENT 5 Sheets-Sheet 2 Filed Sept.9, 1960 OIL WATER-'H R 1 s M m H MLVHK N NLER R E 0 V T Nmm T I M A .K wOR LE WADMM RNE EOR MDF Y B A ril 2, 1963 M. H. GASKELL ET Al. 3,

CELLAR OIL RECOVERY BY WATER DISPLACEMENT Filed Sept. 9, 1960 sSheets-Sheet :5

OIL

WATER INVENTORS. MERWIN H. GASKELL, DONALD C. LINDLEY, FREDERICKMH-PERKIINSJR,

/ E A A, ATTORNEY.

United States Patent 3,083,764 CELLAR OIL RECOVERY BY WATER DISPLACEMENTMerwin H. Gaskell, Donald C. Lindley, and Frederick M. Perkins, Jr.,Houston, Tex., assignors, by mesne assignments, to Jersey ProductionResearch Company,

Tulsa, Okla, a corporation of Delaware Filed Sept. 9, 1960, Ser. No.55,029 2 Claims. (Cl. 1669) This invention concerns recovery of oillocated below the structurally lowest well in reservoirs in which anatural water drive is not present.

Small, steeply inclined reservoirs without natural water drives areoften found associated with salt domes or other highly faultedstructures. Frequently, only one well may be economically justified inthese reservoirs and oil is produced by an expanding gas-cap drive or bya dissolved gas drive. Although a large fraction of the oil up-structurefrom the well may be recovered during primary depletion, because ofgravity effects, only a small fraction of the down-dip oil can beproduced. The downdip oil where no natural water drive is present isdefined as cellar oil in contradistinction to attic oil, which is theoil above the structurally highest well in reservoirs where a naturalwater drive is present.

A primary object of the present invention is an improved method for therecovery of cellar oil.

It is possible after producing a reservoir of this type for a period oftime to inject into the reservoir a limited quantity of water. Thistechnique repressurizes the reservoir and moves the oil up-dip by thegravitational segregation of the injected water down-dip. In someinstances in this type of operation, because of perhaps a reducedpermeability to oil adjacent the well, the length of time required forinjection of water and the length of time required for gravitysegregation of water, the total length of time required to produce thereservoir may be excessive, causing subsequent loss of recoverable oil.

It has also been proposed to inject water through perforations locatedin the lower part of the well opposite the lower part of the penetratedportion of the reservoir and isolated from a set of perforations locatedin the upper part of the well opposite the uppermost part of thepenetrated portion of the reservoir and while injecting water into thelower perforations, producing oil from the upper set of perforations.However, this technique is operational only if the pressure gradientscaused by injection of water are sufficiently low to allow gravityacting on the oil and water to maintain the oil-water contact below theupper set of perforations. This condition can be achieved by injectingwater at sufliciently low rates; but once again, the time required fordepleting the reservoir may be prohibitively long.

The method of the present invention overcomes difliculties inherent inthe known techniques for producing cellar oil by injecting water througha tubing string which opens into the lowermost section of the well bore,injecting oil or another suitable fluid through a second tubing stringwhich opens into the center section of the well bore, and producing oilfrom a third tubing string which opens into the uppermost section of thereservoir. The production rate is set to exceed the rate of injection offluid into the center section. The fluid injected into the centersection has the eflfect of blocking ofi water entering through thelowermost section. By proper adjustment of the two injetcion rates andthe production rate, the cellar oil is produced at an economical rate.

The above noted object and other objects of the invention will beapparent from a more detailed description of the invention taken inconjunction with the drawings wherein FIGS. 1, 2, and 3 arecross-sectional views of a Patented Apr. 2?, 1963 well bore penetratingan inclined subsurface reservoir and serve to illustrate the mechanicsof the operation of the method at different stages.

Referring to the drawings in greater detail, in FIGS. 1, 2, and 3 isshown a reservoir :10 inclined at an angle and penetrated by a well pipe11, which is perforated at 12 in the upper portion, at 13 in the centerportion, and at 14 in the lower portion of the reservoir. Three tubingstrings, 15, 16, and 17, are arranged in pipe 11. Tubing string 15extends to and fluidly communicates with upper perforations 12; tubingstring 16 extends to and fluidly communicates with the centerperforations 13; and tubing string 17 extends to and fluidlycommunicates with the lower perforations 14 of pipe 11. A lower packer18 is arranged on tubing string 17 in pipe 11, and sealingly closes offthe space between tubing string 17 and the interior wall of pipe :11between lower perforations 14 and center perforations 13. An upperpacker 19 is arranged on tubing strings 16 and 17 in. pipe 11 andsealingly closes off the space between these tubing strings and theinterior wall of pipe 11 between upper perforations 12 and centerperforations 13.

As seen in FIG. 1, initially, water is injected through tubing string 17into formation 10, through perforations 14 in casing pipe 11, andsimultaneously a fluid such as oil is injected through tubing string 16into reservoir 10 through center perforations 13. The injected oil keepsthe injected water down, and the water works its way along the lowerside of the reservoir underneath the cellar oil and displaces the cellaroil upwardly.

As the injection of fluids is continued, water continues to displacecellar oil upwardly, and as seen in FIG. 2, the cellar oil has begun tomingle with the injected oil above the water level.

The simultaneous production of oil through upper perforations 12 andtubing string 15 in conjunction with continued injection of oil andwater is illustrated in FIG. 3, and [as seen therein, the cellar oil hasbeen forced upwardly by the injected water to adjacent to and above theupper perforations.

In practice, to determine the most desirable rates of water and oilinjection, there will be a first step of short duration of injection ofwater and oil through tubing strings 16 and 17 and production of oilthrough tubing string 15. The oil production is restricted. to a verylow rate to ascertain that the water is all being directed downstructureby the injection of oil in the center region of the well bore throughpipe string 16 and center perforations 13 in the center region of thewell bore. This operational phase is stopped when fresh reservoir oilappears in the production stream flowing through tubing string 15. Theappearance of fresh reservoir oil is recognized by a change in thegas-oil ratio, since the injected oil will be dead; i.e., free ofdissolved gas. In this phase, water may be injected at a high rate; theoil is injected only in sufficient amounts to block the water injectedfrom rising up-structure. Following completion of this step, the ratesof injection are controlled by the desired rate of production of net oilfrom the well. The rate of water injection equals the net rate of oilproduction, and the rate of oil injection is adjusted so that it is justsuflicient to prevent water production. Oil is produced in an amountequal to the net oil amount desired plus the volume of oil injected toblock ofi the water, since the well will remain at substantiallyequilibrium conditions. The absolute rates of injection and productionwill vary from well to well and are best determinable in the wellitself.

All of the injected oil will be recovered in this method of operation.The method is not a repressurizing process, and it allows the oil to berecovered at the low pressure existing in the reservoir. Therefore, themethod has substantial economic advantages, 'because it avoids the needfor injecting large volumes of fluids at high pressures.

Having fully described the objects, nature, operation, and method of theinvention, we claim:

1. A method of recovery of cellar oil from an inclined reservoir inwhich no natural water drive is present and which is penetrated by aWell pipe perforated along a portion of its length located in saidreservoir comprising simultaneously injecting water into said reservoirthrough the lowermost perforations in said well pipe to displace oilfrom the lower to the upper portions of said reservoir and injecting oilinto said reservoir through the middle perforations in said well pipeand producing fluids from said reservoir through the uppermostperforations in said well pipe; the rate of Water injection, oilinjection, and oil production being selected such that water-free oil isproduced.

2. A method of recovery of cellar oil from an inclined reservoir inwhich no natural water drive is present and which is penetrated by awell pipe perforated along a portion of its length located in thereservoir comprising initially, simultaneously injecting water into saidreservoir through the lowermost perforations in said well pipe todisplace oil from the lower to the upper portions of said reservoir andinjecting oil into said reservoir through the middle perforations insaid well pipe and producing fluids from said reservoir at a low ratethrough the uppermost perforations in said well pipe until freshreservoir oil appears in the oil produced through the uppermostperforations in said well pipe and then continuing to inject water andoil into said reservoir and produce fluids from said reservoir in thesame way, the rates of injection being controlled by the desired rate ofproduction of net oil from the well, the rate of water injection beingequal to the net rate of oil production, the rate of oil injection beingadjusted to that just suflicient to prevent water production, and theoil produced being equal to the net oil desired plus the volume injectedto block off the water.

References Cited in the file of this patent UNITED STATES PATENTS

1. METHOD OF RECOVERY OF CELLAR OIL FROM AN INCLINED RESERVOIR IN WHICHNO NATURAL WATER DRIVE IS PRESENT AND WHICH IS PENETRATED BY A WALL PIPEPERFORATED ALONG A PORTION OF ITS LENGTH LOCATED IN SAID RESERVOIRCOMPRISING SIMULTANEOUSLY INJECTING WATER INTO SAID RESERVOIR THROUGHTHE LOWERMOST PERFORATIONS IN SAID WELL PIPE TO DISPLACE OIL FROM THELOWER TO THE UPPER PORTIONS OF SAID RESERVOIR AND INJECTING OIL INTOSAID RESERVOIR THROUGH THE MIDDLE PERFORATIONS IN SAID WELL PIPE ANDPRODUCING FLUIDS FROM SAID RESERVOIR THROUGH THE UPPERMOST PERFORATIONSIN SAID